Lithium ion batteries have over the past couple of decades been used in portable electronic equipment and more recently in hybrid or electric vehicles. Initially, lithium ion batteries first employed lithium cobalt oxide cathodes. Due to expense, toxicological issues and limited energy capacity other cathode materials have or are being developed.
One class of materials that has been developed and has been commercially employed is lithium metal oxides comprised of two or more of nickel, manganese and cobalt. These materials generally display a layered structure with a singular rhombohedral phase in which initial high specific charge capacities (˜170 mAh/g) have been achieved when charged to voltages of about 4.2 volts vs Li/Li+. Unfortunately, these materials have suffered from a short cycle life and safety issues related to oxygen evolution under certain conditions resulting in fires.
Li/Li+ represents the redox potential of the lithium reference electrode, which is defined as 0 volts by convention. Consequently, when using an anode other than Li metal, these voltages would be decreased to account for the difference in potential between this other anode and Li metal. Illustratively, a fully charged graphite anode has a potential of about 0.1 V vs Li/Li+. Therefore, when charging the cathode in a battery with a graphite anode to 4.25 V vs Li/Li+, the cell voltage will be approximately 4.15 V.
The cycle life is generally taken as the number of cycles (charge-discharge) before reaching a specific capacity that is 80% of the initial specific capacity. Each cycle for these materials is typically between the aforementioned 4.2 volts to 2 volts. These batteries have also suffered from inconsistencies in performance from one battery or cell to another, even though made from the same materials.
To solve some of the problems, the art has described numerous coatings, dopants as well as blending of other more stable cathode materials such as lithium iron phosphate. Examples include those described in U.S. Pat. Publ. Nos. 2004/0005265; 2004/0096743; 2006/0194112; and 2009/0305132; WO patent appl. Nos. 2008/088180; 2008/091074; 2009/057834; and 2013/016426 and Japanese Pat. No. 9035715A1. Unfortunately, even though these may have improved the safety of LIBs containing the cathode materials comprised of lithium metal oxides containing nickel, manganese, cobalt or combination thereof, the cycle life, battery capacity, or capacity at high rates of discharge were not improved.
Accordingly, it would be desirable to provide a method for forming LIBs having cathodes comprised of lithium metal oxides of nickel, manganese, cobalt or combinations thereof that results in more consistent performance, improved cycle life and greater energy capacity retention at faster charge/discharge rates while also improving the safety of such LIBs.